The instant invention relates to a process for piecing with a spinning device operating with a pneumatic twisting unit, in which a yarn end is backfed from the output side through the twisting unit to a drawing equipment to be then inserted laterally into the pair of output rollers of the drawing equipment, from where it is drawn off through the twisting unit in form of a continuous yarn as the rove is incorporated, and to a device to carry out this process.
In a known process of this type the twisting unit is shifted laterally for piecing, so that its input side becomes accessible (DE-OSen 3,411,577 and 3,413894). A yarn end is then pulled from the bobbin and is introduced into the twisting unit from the output side. A suction pipe is moved to the input side of the twisting unit and pulls the yarn end off through the twisting unit. The twisting unit is then brought back into its spinning position and the yarn segment extending from the twisting unit to the suction pipe is inserted into the output roller pair of the drawing equipment. The spinning process can then be resumed. In this known piecing process it is an advantage that the twisting unit must be shifted laterally for the back-feeding of the yarn end to the drawing equipment. On the one hand, additional space is needed next to the twisting unit for this lateral shifting of said twisting unit which prevents the construction being compact. On the other hand, there is the danger that the twisting unit may not return exactly into its starting position as it is returned, and this would impair the, spinning process and the quality of the yarn.
Since the undisturbed spinning process is to be regarded as the normal state in a spinning device, and the piecing process as an extraordinary situation, terms such as "input side" or "input opening" or "output side" or "output opening" of the twisting unit always refer to this normal state. The "input side" or "input opening" of the twisting unit is thus the side or opening towards the drawing equipment since the yarn in the process of being drawn off reaches the twisting unit on that side in the normal spinning process and leaves the twisting unit on its side away from the drawing equipment.
The "rove", in the sense of the instant invention, is to be taken as being any sliver-like fiber material that can be drawn by means of a drawing equipment and can be fed to the twisting unit, whether or not it has little twist or not. Therefore not only fly roves come under this designation, but also card slivers etc.
It is the object of the instant invention to create a process and a device for piecing a spinning device with a pneumatically operated twisting unit, by means of which a shifting of the twisting unit to back-feed the yarn can be dispensed with, so that a spacesaving construction of the spinning device can be achieved and optimal adjustment of the twisting unit is always ensured for spinning.
This object is attained through the invention in a process of this type in that the yarn end is conveyed through the twisting unit located after the pair of output rollers of the drawing equipment to its input side, in that it is seized there and fed to a grasping device located alongside the drawing equipment, which then draws the yarn end past the output roller pair for later insertion into same. Due to the fact that the yarn emerging from the twisting unit at its input side is seized between the drawing equipment and the twisting unit and is conveyed to a grasping device located alongside the drawing equipment, it is not necessary to shift the twisting unit laterally and the twisting unit can thus always remain in its spinning position.
There must merely be enough space provided along the side of the drawing unit so that a grasping device can be installed which can be moved essentially parallel to the direction of movement of the fiber material and thus requires little space. Due to the fact that the twisting unit also does not change position with respect to the drawing equipment for the piecing operation, an optimal position of the twisting unit in relation to the drawing equipment is ensured before and after the piecing process, so that spinning reliability is increased.
The yarn end which is back-fed through the twisting unit is preferably subjected to a compressed air stream flowing parallel to the nip of the pair of output rollers to convey it to the grasping device. Reliable feeding of the yarn end to the grasping device is thus achieved easily, without precise time control being necessary for this.
If the stream of compressed air which conveys the yarn end to the grasping device is turbulent, the danger exists that the yarn end might be conveyed by the air turbulence past the grasping device which thus cannot seize it. To avoid such malfunctions, the yarn end back-feed through the twisting unit is conveyed to the grasping device by means of a laminar compressed air stream in a preferred version of the process of the invention.
In order to increase the reliability with which the yarn end is fed to the grasping device, a yarn reserve can be alternatively or additionally be provided before the back-feeding of the yarn end through the twisting unit, said yarn reserve being then used up so slowly during back-feeding of the yarn end through the twisting unit into the air stream flowing transversely to the path of the yarn, that the yarn end is held straight while it is being fed to the grasping device by the compressed air stream. The slow dissolution of the yarn reserve causes the yarn end emerging from the input opening of the twisting unit to be gradually seized by the stream of compressed air, so that such a straight-line feeding of the yarn to the grasping device is ensured.
The air stream to which the yarn end is exposed while being back-fed should be as weak as possible so that although it ensures back-feeding, it nevertheless does not dissolve the yarn end. Furthermore, air turbulence should be avoided. For this reason, according to an advantageous characteristic of the process according to the invention, the stream of compressed air is to be switched off as soon as the yarn end has been seized by the grasping device.
At the beginning of the yarn draw-off the individual fibers which detach themselves from the rove have the tendency to catch on the yarn. These individual fibers can however not be incorporated properly and constitute ugly shags and bunching in the finished yarn. If the start of the rove is first fed into a suction device immediately after coming out of the drawing equipment, this rove is subjected to the sucking action of the rove suction as well as to that of the twisting unit when the spinning over-pressure is switched on in the twisting unit. This produces undefined negative pressure conditions in the area between drawing equipment and twisting unit which lead to interference during the piecing process. In order to avoid these disadvantages it is advantageous for the yarn end and the rove to be exposed between the output roller pair of the drawing equipment and the twisting unit to a stream of compressed air which is essentially parallel to the nip of the pair of output rollers upon resumption of yarn draw-off.
If the stream of compressed air directed across the yarn draw-off device remains switched on too long this creates the danger of a thin spot being produced in the newly spun yarn, right after the piecing joint. To avoid this, a further advantageous version of the process provides for the stream of compressed air which was switched on after resumption of yarn draw-off to be switched off even before the yarn end leaves the output roller pair of the drawing equipment.
It has been found that individual fibers which get caught on the yarn being drawn off can be blown away from the yarn with great efficiency if the stream of compressed air is directed tangentially counter to the twist of the core of the yarn extending from the drawing equipment to the twisting unit.
To prevent the back-fed yarn end from untwisting in the air stream while it is subjected to the stream of compressed air directed against the grasping device, a considerably weaker stream of compressed air than the one following resumption of yarn draw-off is preferably provided to act upon the yarn end during yarn back-feeding. The strength of the stream of compressed air is calculated so that the yarn can still be reliably conveyed to the grasping device, but without risk of the yarn end becoming untwisted.
With the passage of time, ever greater deposits accumulate in the twisting unit during the spinning process, coming loose from time to time so that they risk being pulled along by the yarn being drawn off. For this reason the twisting unit is preferably cleaned in combination with the piecing process before or during back-feeding of the yarn. This cleaning can be effected in principle by compressed air prevailing in the twisting unit, even before the yarn end is introduced into the twisting unit to be back-fed to the drawing equipment. Such cleaning can however also be combined with the back-feeding process, for example by using a brush for the back-feeding of the yarn end.
Back-feeding of the yarn end can however be effected with the greatest ease, according to the instant invention, by bringing said yarn end by means of a stream of compressed air from the output side of the twisting unit through said twisting unit and into the range of the stream of compressed air acting transversely to the path of the yarn.
Simple control of the compressed air stream acting transversely to the path of the yarn can be obtained according to the instant invention by allowing said compressed air stream to flow during pneumatic back-feeding of the yarn end through the twisting unit only for as long as the compressed air stream causing the yarn back-feeding action prevails within the twisting unit.
The grasping device is preferably pneumatic, whereby a negative pressure is produced in it at least for the time during which the yarn end is being inserted into the drawing equipment. Such a pneumatic grasping device offers the advantage that it is able to securely take away a yarn end produced by yarn breakage and also that it can serve to remove fibers which are blown off after resumption of the yarn draw-off.
The insertion of the yarn end into the drawing equipment can be effected in principle in different ways. For example, the oblique position of the grasping device which is drawn back parallel or at an angle to the path of the fiber material, may already suffice for this. To obtain also timely defined insertion of the yarn end into the output roller pair of the drawing equipment, provisions are made in an advantageous version of the process according to the instant invention for the fiber end to be pulled in form of a loop into the area between the last two pairs of rollers of the drawing equipment after having been pulled alongside the drawing equipment. It is advantageous for the yarn end to be brought simultaneously into the effective range of a yarn brake as it is pulled in form of a loop into the area between the last two roller pairs of the drawing equipment. This ensures that the yarn end cannot suddenly contract after being released by the grasping device and thus assume a position which would not be parallel to the rove, which would lead to a fault in the piecing joint.
In order to achieve reliable and defined insertion of the yarn end into the pair of output rollers of the drawing equipment, suitable provisions can be made for the yarn end to be brought into the zone of the nip of the pair of output rollers during insertion into the drawing equipment.
According to a preferred version of the process according to invention, the twisting unit is cleaned by a first stream of compressed air directed in the direction going from the output edge of the twisting unit to its input side. The yarn end is then subjected to this first stream of compressed air for the purpose of back-feeding to the input side of the twisting unit to be subjected there to a second stream of compressed air acting transversely to the direction of conveyance and which then feeds the yarn end to a grasping device which then pulls the yarn end past the pair of output rollers until it is at the side of the drawing equipment. The previously stopped rove is then released and is sucked away between the drawing equipment and the twisting unit. Following this, the yarn end extending to the grasping device is fed in form of a loop in the area between the last two pairs of rollers of the drawing equipment to a yarn brake and is at the same time inserted into the pair of output rollers of the drawing equipment. The yarn end is now again subjected to draw-off. At the same time the rove and loose fibers are prevented from being sucked into the twisting unit by switching on the second stream of compressed air. Following this, and before the yarn end has reached the pair of output rollers of the drawing equipment, the suction of the rove and the second compressed air stream are switched off.
According to a further, also very advantageous process, the twisting unit is cleaned by a first compressed air stream flowing counter to the direction of draw-off and the yarn end is then subjected to this first compressed air stream and is brought by it from the output side of the twisting unit to its input side. There, the yarn end is subjected to a second compressed air stream acting transversely to the direction of conveyance and is fed by it to a grasping device which pulls the yarn end past the pair of output rollers until it is the side of the drawing equipment. The yarn end extending to the grasping device is then fed in the area between the last two pairs of rollers of the drawing equipment in form of a loop to a yarn brake and is at the same time inserted into the pair of output rollers of the drawing equipment and is once more drawn off. The previously stopped rove is then released while the rove and loose fibers are prevented from being sucked into the twisting unit by switching on the second stream of compressed air. When the yarn end has been pulled out of the drawing equipment for a predetermined length, the suction of the rove as well as the second compressed air stream are again switched off. Finally the spinning over-pressure taking effect within the twisting unit is also brought to bear in the direction of draw-off.
To carry out the process, a device with a pneumatic twisting unit, a back-feeding unit to back-feed the yarn end from the output side of the twisting unit to its input side and with grasping device to pull back the yarn end from the input opening of the twisting unit, past the pair of output rollers up to the side of the drawing equipment, is provided according to the invention with a yarn presenting device to seize the yarn end emerging from the input side of the twisting unit during back-feeding and to feed it to the grasping device. This yarn presenting device makes it unnecessary for the twisting unit to be shifted laterally for piecing.
The yarn presenting device is preferably made in form of a compressed air nozzle oriented essentially at a parallel to the nip of the pair of output rollers, with its output located on the side of the twisting unit across from the grasping device and turned towards said grasping device.
It has proven advantageous for the twisting unit to be provided with an axial projection at its input side and for the compressed air nozzle to be installed relative to the twisting unit in such manner that the stream of compressed air leaving the compressed air nozzle is tangent to the face of said projection. In this manner the air stream is deflected in the direction of the twisting unit in the area following the projection due to the turbulence created. This causes the yarn end to be removed somewhat from the pair of output rollers of the drawing equipment and this improves security during the feeding of the yarn.
For the twisting unit to be located as close as possible to the rollers of the pair of output rollers, this having been shown to be advantageous for the spinning process, provisions are made in a further embodiment of the device according to the invention for the compressed air nozzle to be located at least partly within the nip of the pair of output rollers of the drawing equipment on the side of the twisting unit. In order to prevent fluff from settling on the upper roller of the pair of output rollers of the drawing equipment, a distance of at least 1 mm is preferably provided between the compressed air nozzle and this upper roller.
The reliability with which the yarn is fed from the twisting unit to the grasping device is increased by a laminar compressed air stream. For this reason, a further preferred characteristic of the invention provides for the output of the compressed air nozzle to have an inside diameter of constant cross-section.
It has been shown to be of special advantage for the compressed air nozzle to be arranged tangentially to the yarn end extending from the drawing equipment to the twisting unit so that the compressed air nozzle is oriented counter to the direction of flow of the compressed air which causes the core twist of the yarn end which is produced by the compressed air bores in the twisting unit. This ensures that the compressed air stream prevents the rove or individual fibers from being pulled into the twisting unit by the yarn end when yarn draw-off has been resumed but before the yarn end has left the drawing equipment.
If a twisting unit with only one single row of compressed air bores opening out tangentially into the axial bore is used, the compressed air nozzle is here oriented tangentially to the prolongation of the axial bore of the twisting unit in a direction opposite to the direction into which the compressed air leaving the compressed air bores flows. If, on the other hand, a twisting unit with two rows of compressed air bores behind each other, of which one row opens out into one peripheral direction and the other row into the opposite peripheral direction into the axial bore of the twisting unit is used, the instant invention provides for the compressed air nozzle to be oriented tangentially to the extended axial bore of the twisting unit in a direction opposite to that peripheral direction into which the compressed air bores of the second row, in the sense of yarn draw-off, let out into the axial bore of the twisting unit.
Since it was shown to be advantageous for the feeding of the yarn end to the grasping device to use as weak an air stream as possible, so that the yarn end does not become untwisted, while a stronger over-pressure is better to blow away individual fibers or the start of the rove from the yarn end being drawn off, a further embodiment of the device according to the invention provides for the compressed air nozzle to be provided with a device for selective application of higher or lower over-pressure.
It is advantageous to control the compressed air nozzle in function of the yarn length which is still present in the drawing equipment. For this reason the compressed air nozzle is suitably provided with a control device and the grasping device with a yarn monitoring unit connected to this control device.
According to a preferred embodiment of the invention, the twisting unit is provided with compressed air bores in addition to the compressed air bores in which over-pressure prevails during the spinning process and which have a component in the direction of draw-off, whereby over-pressure is applied in these additional bores during back-feeding of the yarn and said additional bores having a component in direction of back-feeding. These compressed air bores oriented in back-feeding direction can be subjected to over-pressure for the back-feeding of the yarn end as well as for the cleaning of the twisting unit.
If a twisting unit equipped with an injector nozzle and a twisting nozzle in a row and with a gap between them in yarn draw-off direction, is used for the pneumatic back-feeding of the yarn end through the twisting unit up to the area of the yarn presenting device, there is a danger that the yarn end might get caught in the area between the two nozzles of the twisting unit as it is back-fed. To prevent this, provisions can be made in a further advantageous embodiment of the device according to invention for the injector nozzle as well as the twisting nozzle to be provided with a compressed air bore each, oriented in direction of back-feeding, whereby a stronger air stream can be produced in the injector nozzle than in the twisting nozzle. This can be achieved in different ways, for example through an inclination of the compressed air bore in the twisting nozzle that is different than that of the compressed air bore in the injector nozzle. Preferably for this purpose the compressed air bore in the injection nozzle has a diameter which is larger than that of the compressed air bore in the twisting nozzle.
Since in pneumatic back-feeding of the yarn end the compressed air nozzle need take effect only for the duration of back-feeding in order to prevent untwisting of the yarn end, a simple and practical embodiment of the object of the invention provides for the compressed air bores of the twisting unit and of the compressed air nozzle causing the back-feeding of the yarn end to share one common supply circuit as well as one common control valve.
It is not absolutely necessary for the yarn to be fed back pneumatically through the twisting unit into the area of the yarn presenting device. In an alternative embodiment of the device according to the invention it is also possible to provide for a mechanical threading unit for the back-feeding of the yarn end through the twisting unit and into the lifting range of the yarn presenting device. This threading element is then preferably made in form of a clamp. However an alternative advantageous design of the mechanical threading element is also possible by making it in form of a brush which can be equipped with a stripper. A brush has furthermore the advantage, as compared to a threading element in form of a clamp, that said brush could brush off accumulations that may have been deposited in the axial bore of the twisting unit as it is imparted a relative movement within the twisting unit, and could thus clean the twisting unit.
In order to feed the yarn end in a straight line to the grasping device, and thereby ensuring secure reception of the yarn end by the grasping device, it is advantageous for the yarn end to be back-fed slowly through the twisting unit. In addition it is preferable for the back-feeding length to be defined, so that the length of the piecing joint can also be determined easily in advance. To achieve this goal, a yarn reserve device with a drive is advantageously provided on the output side of the twisting unit, whereby said drive drives the yarn reserve device so slowly that the yarn end leaving the input opening of the twisting unit is straightened by the yarn presenting device during feeding to the grasping device. In principle, different designs are possible for the grasping device, e.g. in form of a pair of rollers which seizes the yarn in the manner of a clamp and draws it out of the twisting unit through its rotation and which, upon an axial shift of the grasping device so that the yarn is held even after being released by the pair of rollers, brings it into range of a stationary suction air opening. However, the preferred design for the grasping device is that of a suction air nozzle which is provided advantageously with a suction opening directed towards the yarn presenting device.
The grasping device not only serves to grasp the yarn end fed to it by the yarn presenting device, but also to insert this yarn end into the pair of output rollers of the drawing equipment. In principle, this too can be done in a variety of ways, for instance with a grasping device made in form of a suction air nozzle where the yarn end emerges through a first covered and later opened slit and thus comes within reach of a yarn inserting device which then inserts the yarn end into the drawing equipment. Suitably, the grasping device is however capable of being moved from a receiving position, in which it works together with the yarn presenting device, into an insertion position at the side of the drawing equipment.
The yarn end can in principle be inserted into the drawing equipment by means of an appropriate movement of the grasping device, but a yarn inserting device is preferably provided for this, said yarn inserting device being capable of being moved from a readiness position at the side of the drawing equipment into an insertion position in such manner that it crosses the path of the yarn end extending from the twisting unit to the grasping device and introduces it in its subsequent movement into the drawing equipment. In this area of the drawing equipment a yarn brake to which the yarn end can be conveyed in its insertion movement, is suitably provided. The yarn end can be retained by this yarn brake even after release by the grasping device, so that a parallel position of the yarn end in relation to the rove is ensured during the entire yarn draw-off movement.
The yarn brake can be located in principle at any point of the yarn path between grasping device and the pair of output rollers of the drawing equipment; every effort is made however to install this yarn brake as close as possible to the pair of output rollers of the drawing equipment so that the yarn end is controlled practically over the entire distance between grasping device and the pair of output rollers. For this reason, this brake is advantageously located between the last two pairs of rollers of the drawing equipment. It is especially advantageous if the yarn inserting device and the yarn brake together constitute an elastic yarn clamp when the yarn inserting device is in its inserting position. The yarn brake against which the yarn inserting device presses the yarn end is preferably equipped with a clamping surface made of soft rubber or felt.
In order to ensure rapid introduction of the yarn end into the pair of output rollers of the drawing equipment, provisions are made in a further embodiment of the device according to the invention for the upper roller of the pair of output rollers of the drawing equipment to be provided with a yarn guide which holds the yarn end during pull-back to the side of the drawing equipment up to the moment of insertion into said drawing equipment into the half of the face of the upper roller which is turned towards the nip of the pair of output rollers. This can be achieved in a simple embodiment by giving the yarn guide the form of an essentially cylindrical projection of the upper roller on its side towards the grasping device, whereby the diameter of the projection is smaller than the diameter of the upper roller. Rapid introduction of the yarn end into the pair of output rollers can be assisted furthermore by providing the upper roller of the pair of output rollers with one or several notches between casing surface and face in its edge towards the grasping device.
With spinning machines it is customary today to carry out piecing with the help of a piecing carriage which travels alongside a machine having a plurality of identical spinning stations. When the device according to the invention is used in combination with a machine having a plurality of such spinning stations, it is of special advantage here too for one or several of the elements required solely for the piecing process to be installed on such a piecing carriage.
The instant invention makes it possible to carry out piecing in a reliable manner without changing the arrangement and mounting of the elements required for the normal spinning process and allows for spacesaving construction. The invention makes it futhermore possible to control the piecing process precisely in such a way that the length of the piecing joint in the yarn can be kept very short and can be predetermined exactly. In this way unobtrusive and strong piecing joints are obtained in the yarn.
The device according to the invention is at the same time simple in its construction and greatly facilitates the utilization of a piecing carriage since it is not necessary to adjust machine elements at the twisting unit or drawing equipment to carry out the piecing process. An electric control of air pressures or a rove stopping device which in any case can be controlled from the spinning station in case of yarn breakage is sufficient here. All other elements, required only for piecing, can be installed on the piecing carriage.